How Myxozoan Mitochondrial Genomes Evolved

Jenn Hoskins
24th April, 2024

How Myxozoan Mitochondrial Genomes Evolved

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Tel Aviv University sequenced mitochondrial genomes of five myxozoan species, parasites affecting fish
  • The study found that these myxozoans have a circular mitochondrial chromosome, suggesting a common ancestral genome structure
  • Loss of mitochondrial genes, including those for cellular respiration, is not widespread among myxozoans, contrasting with previous findings in one species
Understanding the evolutionary relationships among species is a crucial aspect of biology, as it helps scientists uncover the history of life and the intricate connections between different organisms. One particularly interesting group in this regard is the Myxozoa, a class of microscopic parasites that have puzzled scientists for years due to their complex life cycles and reduced physical forms. These parasites, which have a significant impact on both aquaculture and wild fish populations, are known to have a close relationship with the cnidarian family, which includes more familiar organisms like jellyfish and corals[2]. Recent research conducted by scientists at Tel Aviv University has made significant strides in unraveling the phylogenetic relationships within the Myxozoa[1]. Previously, the evolutionary history of these organisms has been contentious, largely because they lack distinctive physical features and there has been a scarcity of molecular data to analyze[3]. Mitochondrial genomes, which are DNA sequences inherited only from the mother and are found in the mitochondria of cells, have been used in many other organisms to establish evolutionary relationships. However, only five complete mitochondrial genomes of myxozoans had been sequenced before this study, leaving a gap in our understanding. This new study aimed to fill that gap by sequencing the mitochondrial genomes of five additional myxozoan species. This was a significant undertaking because it could clarify whether the loss of certain mitochondrial genes, observed in some myxozoan species, is a common trait within the group. Specifically, previous research had found that while some myxozoan species had cytochrome oxidase genes—important components for cellular energy production—others like Myxobolus squamalis did not, and one species, Henneguya salminicola, had lost its entire mitochondrial genome. The researchers used advanced DNA sequencing technologies, including Illumina and Oxford Nanopore platforms, to sequence the mitochondrial genomes of Myxobolus wulii, M. honghuensis, M. shantungensis, Thelohanellus kitauei, and Sphaeromyxa zaharoni. By doing so, they hoped to shed light on the utility of mitochondrial genomes for reconstructing the relationships among myxozoans and to understand the apparent gene losses in some species. The findings from this study have the potential to significantly advance our understanding of myxozoan evolution. They build upon earlier phylogenomic analyses that confirmed myxozoans as cnidarians and identified them as a sister taxon to another cnidarian parasite, Polypodium hydriforme[2]. These earlier studies also revealed that myxozoans have some of the smallest animal genomes and have undergone extreme reductions in both genome size and gene content as they transitioned from a free-living cnidarian to a microscopic parasitic form[2]. Additionally, the circular structure of the mitochondrial genome of P. hydriforme supported the view that it is a sister clade to Myxozoa, rather than being part of the Medusozoa, as previously thought[4]. By adding five more complete mitochondrial genomes to the myxozoan dataset, the Tel Aviv University researchers are helping to clarify the evolutionary trajectory of these parasites. The study may also provide insights into how these organisms have adapted to their parasitic lifestyle, including the biological significance of gene losses, such as the cytochrome oxidase genes and, in one remarkable case, the entire mitochondrial genome. The implications of this research are far-reaching. Not only does it help to resolve the phylogenetic placement of myxozoans within the animal kingdom, but it also contributes to our understanding of how parasites evolve and adapt to their hosts over time. The loss of mitochondrial genes, for instance, might reflect a deep level of dependency on their hosts for survival, which could have implications for disease control and management in fisheries. Moreover, the study's findings could inform future research on the evolutionary mechanisms that enable such drastic genomic reductions in other parasitic species. In summary, the research from Tel Aviv University provides a clearer picture of the evolutionary history of myxozoans by expanding the available mitochondrial genomic data. This work not only enhances our knowledge of these unique parasites but also contributes to the broader understanding of parasite-host relationships and the evolutionary processes that shape them.



Main Study

1) Evolution of myxozoan mitochondrial genomes: insights from myxobolids

Published 22nd April, 2024

Related Studies

2) Genomic insights into the evolutionary origin of Myxozoa within Cnidaria.

3) The joint evolution of the Myxozoa and their alternate hosts: A cnidarian recipe for success and vast biodiversity.

4) The Phylogenetic Position of the Enigmatic, Polypodium hydriforme (Cnidaria, Polypodiozoa): Insights from Mitochondrial Genomes.

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